W140 can't loosen brake line
 

I'm trying to swap out the master cylinder on my 1998 S320. I can't get the rear brake line fitting loose. I am using a proper flare wrench but it won't budge. Any tips? These things aren't reverse thread or anything crazy like that, are they? I haven't tried to loosen the other fitting yet. Rounding off one would be bad enough. :mad: (Which I haven't done yet, but got close.)

When removing flare nuts on the brake lines of older cars, I have had same problem. The flare wrenches were sometimes not a good fit. I sometimes used a special vice-grip that is designed to grip hex heads along with a piece of tube to increase leverage. Whatever, you need something that fits the head and won't slip and round it. I have also just cut the tubing and used a ring spanner (box end wrench). But only when I could replace the tube easily with a short length.

To get the nut to release, I have used one of those small butane torches. Just heat the nut, try to turn. Repeat until it comes loose. Brake fluid can take a high temperature, so don't worry about that. But keep flame away from rubber parts.

If I could find a part number for the hard lines from the MC to the ABS pump, I'd just cut the old ones and install new. So far I haven't found an online source that lists those. Going to call the dealer in the morning and see if it's available.

When working on my W123, I found that even dealer only sold brake lines in straight pieces. Not bent to shape.

You can buy cupro-nickel brake lines with the ends already swaged. They are not expensive and can easily be bent by hand to shape needed. This is not true of steel lines where you need a tube bender. You do need to make sure you use tubes fitted with Euro bubble flare ends. The tubes come in various lengths for example 8",12",20", etc up to 60". In one case I used two with a joiner to get just the right length.

I bought mine from local parts store in Canada. I am sure they are also available at US parts stores. For example:
CARQUEST - 3/16" Nicopp Brake Lines - European (Nickel/Copper

Well, I went all out and ordered one from the dealer. Probably spent way more than I needed to ($48 USD), but the convenience of knowing the flares are the correct size and it's the right length is worth it to me. I end up wasting so much time researching stuff online and driving back and forth. This way even if I have to bend it I've still eliminated part of the guesswork.

I'm going to pick up a crowfoot line wrench to see if I can get a better grip on the nut. One corner had already been rounded off a little, but it's the only one I can get leverage on with a regular wrench. I'm hoping with a crowfoot on a ratchet extension I can rotate it and get it onto the corners that are in better condition. But I'm going to leave it alone until I have parts in hand, just in case.

FYI - the crowfoot did the trick. Popped it right off. Best $11.99 I ever spent.

Great. Good work!
I have a set of crowfoots. I liked the fact that they were a tight fit and that the jaws were quite thick. I didn't like the offset drive that mine have, but heck if they worked, that's the main thing!